1. Field of the Invention
The present invention relates to a single-side polishing method for a substrate edge and to an apparatus therefor. More particularly, the invention relates to a single-side polishing method for mirror-polishing an edge of a disk-shaped substrate such as a semiconductor wafer, a glass plate, a quartz plate, or a ceramic substrate, which is an outer periphery of such a disk, or mirror-polishing an edge of a disk-shaped substrate having an oxide film or an insulating film on one side thereof, for removing an insulating film or the like, typically represented by an oxide film, outside the outermost pattern.
2. Description of the Related Art
A wafer used as a substrate for a semiconductor device is manufactured, for example, by slicing a single-crystal ingot such as a silicon ingot, perpendicularly to the axial direction, beveling the resultant slice, and subjecting the same to processes such as lapping, etching, annealing, and polishing.
Beveling carried out in the wafer manufacturing process as described above has a primary object of preventing chipping at the edge of the wafer, and a method of grinding off the wafer edge by means of a high-rigidity grindstone is usually adopted for beveling.
Along with the recent trend toward higher densities in semiconductor devices, however, the measures taken to prevent the generation of dust in the manufacturing process have become more strict. For the wafers, as a material therefor, the absence of dust has become an important requirement, resulting in an increasing necessity to polish the wafer edge to an extent equal to that of the mirror-polished portion of the wafer.
For a wafer having a pattern such as an oxide film or an insulating film formed on a side of the wafer, dust is produced at the oxide film or the insulating film of the one-side edge and this may exert an adverse effect. It is therefore necessary to previously eliminate the possibility of dust occurrence by removing the oxide film or the insulating film located outside the outermost pattern, and for this purpose, the upper edge of the wafer must be polished.
Known polishing apparatuses for polishing the edge of a wafer into a bevel include those disclosed in Japanese Patents Nos. 2815797 and 2889108.
The apparatus disclosed in Japanese Patent No. 2815797 has a configuration in which an arcuate polishing groove, having a radius of curvature substantially agreeing with the outer periphery of the wafer edge, is formed in a polishing buffer, and the outer periphery of the wafer, i.e., the wafer edge, is pressed into this arcuate polishing groove for polishing.
The apparatus disclosed in Japanese Patent No. 2889108 has a configuration in which a polishing tape housed in a coiled form in a rotary drum is payed out onto the peripheral surface of the rotary drum and is coiled again in the drum after passing around the drum. The wafer edge is polished at a portion of the polishing tape located on the peripheral surface of the rotary drum, and during polishing, the rotary drum is tilted at a prescribed oscillation angle in the forward/backward direction by an oscillating means.
In the apparatus disclosed in Japanese Patent No. 2815797 in which the arcuate polishing groove substantially agreeing with the wafer edge is formed in the polishing buffer itself and polishing is accomplished by pressing this arcuate polishing groove against the wafer edge, however, it is necessary to press the arcuate polishing groove against the wafer edge in a constant direction. When a shift occurs in this direction, the polishing of the wafer edge becomes unstable.
When the arcuate polishing groove is formed in the polishing buffer, it is necessary to provide a plurality of grooves because there are various beveled shapes of the wafer edges to be polished, thus requiring complicated operations.
The shape of the arcuate polishing groove is gradually worn away. Various problems therefore arise, for example, in that excessive wear may result in polishing not only of the wafer edge, but also of the flat portion of the wafer.
In the apparatus disclosed in Japanese Patent No. 2889108, on the other hand, it is necessary to tilt the rotary drum in the forward/backward direction during polishing, requiring a complicated tilting mechanism to produce this tilting. Other problems are the large size of the apparatus itself and higher cost.
There is also available an apparatus in which grooves of various sizes are arranged in the polishing strip located outside the supporting section, and polishing is conducted by pressing the wafer edge against an appropriate groove. In this apparatus, the shape of the groove may be changed by polishing, resulting in disagreement between the groove and the wafer edge, thus making it impossible to carry out satisfactory polishing.
All the aforementioned apparatuses are designed to simultaneously polish the upper and lower sides of the wafer edge, and they are not therefore suitable for polishing only a single side of the wafer edge.
Japanese Unexamined Patent Application Publication No. 7-193030 discloses an apparatus using a polishing strip not having a groove formed thereon. In this apparatus, only a single side of wafer can be polished by removing a lower side driving roller. However, because grinding grains are embedded in the polishing strip, the wafer is not polished but ground by moving the polishing strip provided with these grinding grains relative to the wafer edge. It is therefore necessary to continuously move the polishing strip during grinding. Upon discontinuation of movement, therefore, the grinding grains coming into contact with the wafer at that moment, leaving grinding marks. In order to remove the polysilicon film, the configuration must be as described above.
In the apparatus proposed in the present invention, in contrast, having a configuration in which a substrate edge is polished, grinding grains are not embedded in the polishing strip itself, and the polishing strip is stopped during polishing. Thus, the object of the invention is quite different from the object of the aforementioned Japanese Unexamined Patent Application Publication No. 7-193030.
The conventional apparatuses have various problems as described above, and furthermore, it is necessary to mirror-finish the entire surface of a wafer by a polishing apparatus. It is therefore necessary to reduce portions in contact with the wafer on the supporting mechanism supporting the wafer itself, and to minimize the contact portions when supporting the wafer.
The present invention has as an object to provide a single-side polishing method for a substrate edge and an apparatus therefor, which permit polishing of an edge of a substrate by pressing a polishing strip (a narrow pad) against the edge of the substrate such as a wafer to be polished, and do not require tilting of the substrate during polishing, thus eliminating the necessity of a tilting mechanism, and allow reduction in size of the overall apparatus and lower cost.
Another object of the invention is to provide a single-side polishing method for a substrate edge and an apparatus therefor which permit polishing of an edge of a substrate by pressing a polishing strip (a narrow pad) against the edge of the substrate, such as a wafer, to be polished, and do not require tilting of the substrate during polishing, thus eliminating the necessity of a tilting mechanism, and allow reduction in size of the overall apparatus and lower cost, and which make it possible to adjust the pressing force acting during polishing of the substrate edge to achieve a desired polished condition, and to ensure polishing of a desired portion even when a pattern such as an oxide film or an insulating film is formed on a single side.
To achieve the above-mentioned objects, the invention provides a single-side polishing method for a substrate edge, comprising the steps of bringing a moving section having a surface coming into contact with a substrate edge in the presence of a polishing strip and given a force by a force imparting member with a side of the substrate edge rotatably held by a substrate holding member, to press the polishing strip against the side and an end face of the substrate edge, and rotate the substrate for polishing the side and the end face of the substrate.
The invention provides a single-side polishing apparatus for a substrate edge, comprising a substrate holding member rotatably holding a substrate, and a supporting member capable of relatively coming into contact with and retreating from the substrate holding member, wherein a moving section coming into contact with a single side and an end face of the substrate edge in the presence of a polishing strip is additionally provided.
The invention provides another single-side polishing apparatus for a substrate edge, comprising a substrate holding member rotatably holding a substrate, and a supporting member capable of relatively coming into contact with and retreating from the substrate holding member, wherein the supporting member comprises a fixing section to the substrate and a vertically movable moving section; the moving section, given a force by a force imparting member, is capable of coming into contact with a side of the substrate edge; and furthermore, a polishing strip, positioned between the moving section and the substrate, comes into contact with the side and an end face of the substrate edge.
In the apparatus of the invention, the polishing strip is located on one side of the moving section when it is wound and stretched to cause the end to be sequentially payed out, and after covering the lower surface of the leading end of the moving section, the end is positioned on the other side of the moving section and is sequentially taken up, and paying-out and coiling of the polishing strip are discontinued during polishing when it is pressed against the substrate edge and the lower surface of the moving section.
Since the above-mentioned means are adopted in the present invention, and as a result, a side and an end face of the edge of the substrate rotate while pressing the polishing strip provided on the supporting member, the side and the end face of the substrate edge are certainly polished by the polishing strip.
Furthermore, because the polishing strip is pressed by the moving section give a force by the force imparting member, a portion of the substrate edge can be polished in response to the shape of the moving section.
The polishing strip can be payed out and coiled. New portions of the polishing strip can therefore be brought into contact with the substrate edge for polishing by discontinuing movement of the polishing strip, and paying out and coiling it during non-polishing periods.